1. Field
The present disclosure relates to tires for heavy goods vehicles, and more particularly to tires intended for fitting to heavy goods vehicles.
The present disclosure relates to a tire with a radial carcass reinforcement, intended for fitting to heavy vehicles such as lorries, buses, tractors, trailers and the like, and relates more particularly to the crown reinforcement of this tire in combination with its tread.
Generally, the radial carcass reinforcement of the tire in question, formed by inextensible metal or aromatic polyamide reinforcing elements, is surmounted on the radially outer side by a crown reinforcement comprising a plurality of crown plies. In a well-known embodiment, the crown reinforcement comprises a triangulation ply formed by metal elements orientated at an angle in the range from 45 to 90 degrees relative to the circumferential direction, said triangulation ply being itself surmounted by two working plies formed by inextensible metal reinforcing elements, parallel to each other in each ply and crossing over from one ply to the next, forming angles in the range from 10 to 45 degrees with the circumferential direction. These working plies, forming the working reinforcement, are covered with at least one ply called the protection ply, which essentially serves to provide protection for the working plies against damage that may be caused by foreign bodies penetrating into the grooves of the tread.
This ply may be formed by metal reinforcing elements called “extensible” or from elements called “elastic”, that is to say those whose force-elongation curve shows a relatively large elongation under a low tensile force. In this case, the reinforcing elements of the protection ply are generally orientated in the same direction and at the same angle in absolute terms as the reinforcing elements of the radially outermost working ply, and are generally axially narrower than the radially outermost working ply. This protection ply may be made of any material and with any structure which serves the purpose of protecting the working reinforcement; a homogeneous material in the form of circumferentially wound bands or a ply may be considered.
In combination with this internal reinforcement structure, there is a known way of providing the tread, that is to say the part of the tire intended to come into contact with the ground as it rolls and to become progressively worn, with a tread pattern formed of grooves and slits.
In the present application, the slits are distinguished from the grooves in that the slits are narrow, generally allowing contact between the facing walls that delimit them during running, and notably during passage through the footprint, which would not be the case for the grooves in normal conditions of use of the tire.
2. Description of Related Art
The document US-20100269967-A describes a heavy goods tire comprising a radial carcass reinforcement surmounted by a crown reinforcement, centered on the equatorial plane, which is itself surmounted by a tread. This reinforcement comprises a plurality of working plies surmounted by a protection ply whose width is substantially smaller than the width of the narrowest working ply. This protection ply is located radially within two grooves arranged symmetrically about the equatorial plane. Axially outside these two grooves, the tread is provided on each side with a groove having the same depth as the other two grooves. In order to have high performance in terms of endurance, this structure requires the presence of a minimum thickness between the bottom of the grooves and the last of the working plies in the region located axially beyond the protection ply.
The document WO 2011/002454 describes a tire produced by retreading, this tire comprising a carcass surmounted radially externally by a crown reinforcement, which is itself surmounted by a pre-vulcanized tread. This tread comprises a plurality of grooves opening on the outside and grooves opening on the inner face of the tread. The latter are provided to form new grooves after the partial wear of the tread. The set of inner and outer grooves is placed radially above the set of plies forming the crown reinforcement. The edge rib formed in this way is relatively rigid, since the set of the plies of the crown reinforcement is present therein.
There is a need for a tire structure for heavy goods vehicles which, combined with a tread pattern, allows better optimization of performance in terms of rolling resistance, endurance and levelling in contact with a road, while providing optimal safety regardless of the state of wear of the tire.